1. Field of the Invention
The present invention relates to planarizing a surface of a semiconductor wafer, and more particularly, to a polishing method and apparatus thereof, which satisfies multiple polishing requirements, for polishing the surface of a semiconductor wafer.
2. Discussion of Related Art
Generally, a semiconductor device requires a process for accumulating multiple layers on a semiconductor wafer. In such a process for high integration, it is desirable for a semiconductor device to be made in a limited space. Thus, planarization of a semiconductor wafer surface having multiple layers is an important process and an important parameter in increasing process yields.
A typical method for the planarization of a semiconductor wafer is a Chemical Mechanical Polishing (hereinafter referred to as CMP) method.
A typical CMP apparatus for a semiconductor wafer includes a carrier for holding the semiconductor wafer. Also, the typical CMP apparatus includes a polishing table having a polishing pad. The polishing pad contains a polishing material. The surface of the semiconductor wafer is polished by friction caused by moving the surface of the semiconductor wafer against the surface of the polishing pad having the polishing material. In addition, the more abrasive the polishing material is, the easier the surface of the semiconductor can be polished.
There have been structural improvements to the typical CMP apparatus for enhancing uniformity rate and polishing rate. Such structural improvements are related to the structure of the polishing pad that makes contact with the surface of the semiconductor wafer. One such structural improvement is illustrated in U.S. Pat. No. 5,212,910. The structural improvement is related to the polishing pad structure having complex materials with complex characteristics to improve polishing performance. FIG. 1 shows a cross-sectional structure of the prior art polishing pad of U.S. Pat. No. 5,212,910 used for a CMP apparatus.
As shown in FIG. 1, the prior art polishing pad 11 is formed on a polishing table 10. The polishing pad 11 comprises a first layer 20 composed of an elastic material such as a sponge, and a second layer 22 on the first layer 20. The second layer 22 is divided into sections of a hard material and predetermined empty spaces 29. The polishing pad 11 also comprises a third layer 23 formed on the second layer 22. The third layer 23 is made of a hard material that is used with a polishing solution to polish the surface of the semiconductor wafer.
The semiconductor wafer is polished as a result of the friction caused when the polishing pad 11 rubs against the top surface of the semiconductor wafer. By having the polishing pad 11 on the polishing table 10, the polishing table 10 rotates the polishing pad 11 that causes the polishing pad 11 to rub against the top surface of the semiconductor wafer. Thus, the friction caused from the rubbing action polishes the top surface of the semiconductor wafer. Polishing solution, which is optional, may be applied to the surface of the semiconductor wafer to enhance the polishing process.
However, the top layer of the polishing pad of the prior art, which makes contact with the surface of the semiconductor wafer, comprises of only one type of polishing material. Thus, there are limits in improving the polishing characteristics of one type of polishing material. Also, when a layer formed on the surface of the semiconductor wafer comprises of multiple materials, the polishing pad must satisfy multiple polishing requirements. Thus, having one type of polishing material is deficient for a polishing pad. Further, a polishing pad with one type of polishing material and characteristic is not suitable for satisfying multiple polishing requirements of semiconductor wafers.
Therefore, the polishing pad, which comprises of a top layer of one type of polishing material, cannot properly polish a surface of a semiconductor wafer that requires a different polishing characteristic than the polishing characteristic of the top layer. Thus, in order to solve the difference in polishing characteristics, a new polishing pad with a different top layer having a different polishing material is required. As a result, polishing pads must be replaced on a polishing table, which reduces operation efficiency.